Double clutch transmissions have already been in use in motor vehicles in gearbox transmissions, mainly in automatic transmission systems. They possess the distinction of operating under a nearly pull force free condition when shifting the gear position. Herewith, the accomplishments are more comfortable and fewer load changes during shifting, allowing at the same time a simultaneously, improved acceleration of the vehicle. A frequently used standard construction method utilizing coaxial drive shafts and their function is explained, for instance, in the DE 198 21 164 A1.
Therein, two clutches which are located at the driving end and are for instance wet running plate clutches, in each case these are linked together by means of a transmission's input shaft with a sub-transmission formed as an intermediate transmission, whereby one of the sub-transmissions encompasses the even numbered forward gear positions, and the other sub-transmission encompasses the odd numbered forward gear positions. One or more reverse gear positions can be arranged on either side, depending on the amount of the gear positions.
The two clutches are constructed as an interlaced double clutch, whereby the two transmissions input shafts are arranged in a coaxial formation with each other. One input transmission shaft is in this case constructed as a shorter hollow shaft, bearing concentrically the other transmissions input shaft which is constructed as a central shaft or solid shaft and extends from the hollow shaft in an area opposite of the clutches.
Such transmission's shift operation takes place sequentially, whereby in each case a next following shift position is being preselected by the currently non-transmitting sub-transmission, so that two shift positions are being engaged simultaneously and, through overlaying disengagement or engagement of the two clutches, the shift changes can proceed from the current shift position to the next, targeted shift position, practically without interrupting the vehicle's drive condition.
In general, gear and shift transmissions for vehicles are being increasingly manufactured with a higher amount of gear positions, to increase the efficiency and to make better use of the combustion engine's potential, whereby, at the same time, an attempt is made to reduce the emission of unwanted pollutants. By now, six-position transmissions in passenger cars are quite commonly used. Also, seven-position transmissions are known as conventional transmissions having a clutch, an example can be found in the patent filing DE 103 05 242 A1, and also already known as a double clutch system with two clutches, as shown in the patent filing DE 103 05 241 A1.
Generally, the motor vehicle's transmission with up to seven forward gear positions will be designed as a single-group transmission. While multi-stage automatic transmissions can also be designed with planetary configurations having more than seven gear positions, as described in the patent filing DE 10 2004 041 507 A1, transmissions with even larger gear positions are most likely being designed and constructed with multiple-group configurations. The presently available multiple-group transmissions are predominantly provided for commercial utility vehicles. Hereby, a typical use, for up to 16 forward gear positions, is generally a two-group configuration with one main-group and a following range group, additionally known is a three-group configuration with a preceding split-group.
A multi-group design is also already known in double clutch transmissions. A double clutch system is been described in DE 102 32 831 A1, where the two sub-transmissions in each case include two group transmissions, establishing a 2×2×3 intermediate gear transmission representing a total of 12 forward gear positions.
Furthermore, the winding transmissions are known in the art. The flow of the energy, when shifting between one or more gears in winding transmissions, proceeds through several gear stages, between one main shaft and a parallel counter shaft or counter shaft, respectively. In other words, the flow of energy is “winding” itself through the transmission. A general description of the particular transmissions can be found in G. Lechner, N. Naunheimer: “Fahrzeuggetriebe, Grundlagen, Auswahl, Auslegung and Konstruktion.”, Springer Verlag, Berlin, Heidelberg, 1991. Winding transmissions, as compared to conventional transmission, have the advantage of using fewer gear pairs, can be constructed relatively compact, and can therefore also be considered in the manufacturing of transmission with a relatively high gear count, so called high gear count transmissions. In addition, they can be easily controlled through shorter shift intervals, as compared to multi-group transmissions. In principle, all gears of a winding transmission can be switched and are allocated to their own shafts and rotatable mounted on shafts, respectively, resulting in “r” gear stages and a number of gears equal to z=2r-1. This means that, by using the three gear stages, a four gear transmission can be realized and therefore, compared to a conventional four gear transmission, one gear stage can be spared.
A combination of a group transmission together with a winding transmission is known in the art through DE 101 37 356 A1. In the publication, a two group intermediate transmission is described, with a main group in a winding construction and a preceding section group. The main group comprises three gear sets which are used as the forward gears, as well as a conversion wheel set for the reverse gear. The section group shows two additional gear sets needed for the forward gears. The first gear set in the main transmission is positioned on a drive shaft. The two following gear sets are positioned on a counter shaft, which can be connected through shift clutches on one side with the drive shaft and on the other hand with the section transmission's output shaft. The intermediate gear shaft is separated within the main transmission also at a proper location through a shift clutch. Thereby, different shift combinations can occur, where the flow of energy flows through several gear stages. The first four gear positions, generated by the main winding transmission, are guided through the section transmission's first gear set to the drive shaft, four additional shift positions are accomplished through the section transmission's second gear set. In addition, a 9th gear is available as direct gear, in which the output shaft is coupled with the drive shaft through the counter shaft.
The application of a winding construction in a double clutch transmission is known in itself through DE 103 39 758 A1. The two sub-transmissions are arranged as interlaced units. The double clutch is designed in a conventional construction and is connected on the output side with the outer hollow shaft, as well as with the inner solid shaft. The hollow shaft, through a first input constant, produces in the first sub-transmission the odd gears one, three, five, and seven, as well as two (odd) reverse gears. The solid shaft, through a second input constant, produces gear two, four, and six, as well as an additional (even) reverse gear position.
To generate a direct gear, for example the sixth gear, the solid shaft can be coupled through a first shift clutch with a coaxial drive shaft. The first shift clutch serves for operating two gear sets. A second shift clutch activates a reverse wheel set, but is also, in the direction of the transmission's output, connected to a hollow shaft which contains and additional solid shaft, the hollow shaft carries two gears, where one is switchable through the second shift clutch and the other being switchable through a fourth shift clutch, located opposite on the counter shaft of the first sub-transmission.
Comparable to the transmission input shaft's configuration, the counter shafts of the sub-transmissions are also designed with an outer hollow shaft which contains the inner solid shaft, penetrating the hollow shaft but, in this case, the hollow shaft is assigned to the second sub-transmission and the solid shaft is assigned to the first sub-transmission. The link between the transmission's input shafts and the related counter shafts is achieved through respective input constants. At the end of the transmission's output of the outer, hollow counter shaft, here the second sub-transmission, a third shift clutch is connected, which can selectively connects a gear of the second sub-transmission with the outer counter shaft or it connects the outer counter shaft with the inner counter shaft, meaning the first sub-transmission.
Because of the sub-transmissions' interlaced structure and through a corresponding shift logic, a flow of energy is established for the different gears, which proceeds parallel in the sub-transmissions and in partial sections axial, from the output back towards the input, to be finally re-routed again after several windings towards the output direction. Overall, the known configuration presents a relatively compact double clutch transmission with seven forward gear and three reverse gear positions, which are switchable by a total of four shift clutches.
The focus of DE 103 39 758 A1 is towards establishing a double clutch transmission with several, for instance one even and two odd reverse gear positions, which is especially advantageous to utility vehicles. Hereby, drivel-force-interrupted is perceived when shifting between the reverse gears and/or between forward and reverse gears. The preferred amount of forward gears is an odd number. Because the first gear and the highest gear, under conditions of odd number shift positions, belong to the same sub-transmission, a relatively short first gear can be established through the support of a winding first gear, therefore accomplishing a high input gear transmission ratio which is required for utility vehicles and at the same time offering an adequate, high gear ratio spread for the largest gear.
Disadvantageously, however, with this described transmission structure at least one gear wheel pair can be saved with the conventional intermediate transmission. An increase to a higher number of gear positions than seven is not readily feasible, because of a complicated and elaborate construction and also a complicated flow of energy. A person skilled in the art will not find any hints in it, regarding the realization of a double clutch transmission with more than seven gear positions in the way of winding construction.